Problem
A mirror backup deletes a healthy destination copy after a source-side accidental deletion because replication was configured without immutable or versioned retention.
Solution
Root Cause / Diagnostic:
Simple two-way synchronization or unversioned 1:1 mirroring treats the destination as an exact replica of the source. When a creator accidentally deletes or moves a folder on the primary storage, the next synchronization cycle immediately purges those files from the backup pool, eliminating your safety net.
Actionable Fix:
1. Versioned / Snapshot Retention Configuration: Reconfigure replication software to enforce versioning or snapshot locking (e.g., TrueNAS ZFS replication with immutable snapshots or rsync with `--backup-dir`).
2. Object Lock / WORM Storage Policy: Implement Write-Once-Read-Many (WORM) or S3 Object Lock in compliance/governance mode on the backup repository for a minimum of 30 days.
3. Deletion Propagation Simulation: Conduct a test sync after deleting a temporary test folder on the source to confirm the destination archives or retains the deleted file in a recovery directory.
Pro Tip:
A mirror sync is not a backup; if you accidentally delete a folder on your main drive, a mirror deletes it from your backup too. Always configure snapshots or versioned retention.
Simple two-way synchronization or unversioned 1:1 mirroring treats the destination as an exact replica of the source. When a creator accidentally deletes or moves a folder on the primary storage, the next synchronization cycle immediately purges those files from the backup pool, eliminating your safety net.
Actionable Fix:
1. Versioned / Snapshot Retention Configuration: Reconfigure replication software to enforce versioning or snapshot locking (e.g., TrueNAS ZFS replication with immutable snapshots or rsync with `--backup-dir`).
2. Object Lock / WORM Storage Policy: Implement Write-Once-Read-Many (WORM) or S3 Object Lock in compliance/governance mode on the backup repository for a minimum of 30 days.
3. Deletion Propagation Simulation: Conduct a test sync after deleting a temporary test folder on the source to confirm the destination archives or retains the deleted file in a recovery directory.
Pro Tip:
A mirror sync is not a backup; if you accidentally delete a folder on your main drive, a mirror deletes it from your backup too. Always configure snapshots or versioned retention.